plain-ltx – Make plain TeX files LaTeXable

The pack­age plain.sty de­fines a LaTeX en­vi­ron­ment which can
pro­cess a doc­u­ment writ­ten to use Knuth's ba­sic
Plain TeX macros.

In­side the en­vi­ron­ment, not ev­ery­thing is as Knuth in­tended (some
Plain com­mands are sup­pressed, some are faked, and some ba­sic
mech­a­nisms—such as font se­lec­tion and the out­put
rou­tine—re­main as in LaTeX). Thus “sim­ple” doc­u­ments
will run, but elab­o­rate macros de­fined in the doc­u­ment have a
chance of fail­ing.